How to Fix Office 365 Not Syncing with Outlook Issue?

  

Rollins Duke   
Published: October 10th, 2025 • 6 Min Read

It is frustrating when your office 365 not syncing with outlook, messages are not receiving, folders are not updating and calendar entries are missing. This guide has got you covered. In this comprehensive article, we will guide you step-by-step from quick check to deep fixes to overcome the office 365 email not syncing with outlook error. Additionally, we will show a professional and reliable tool so that you never lose data if it happens again. Let’s start.

Why is Office 365 Not Syncing with Outlook?

Here we will discuss some common reasons why users face office 365 and outlook synchronization errors before jumping to the solutions.

• Unstable or weak internet connection.
• Maybe your OST file is damaged or corrupted.
• Large or oversized mailboxes and folders.
• Outlook set in Offline mode or not in sync mode.
• Older versions may lack compatibility with new Microsoft 365 security.
• Wrong sync settings in Outlook.
• Due to a temporary Microsoft service outage.

Also Read: How to Export Office 365 Mailbox to PST?

How to Resolve Office 365 Email not Syncing with Outlook?

Here, in this section we have mentioned some of the useful and reliable manual fixes that will help you overcome the Outlook Office 365 not receiving email issue. Read and follow them properly to avoid any confusion.

1. Check Internet Connectivity

Make sure you have a stable internet connection. Try to open other websites and keep refreshing Outlook to check if the connection is lost or slow. If you are in a corporate environment, ensure that no firewall or proxy is blocking the Outlook ports, usually 443 for HTTPS.

2. Verify Outlook Offline Mode

Sometimes Outlook is accidentally set to offline mode which results in office 365 outlook synchronization errors. Follow the below steps to switch.

1. Open Outlook.
2. Go to the Send/Receive tab.
3. Check if the option Work Offline is active.
4. If yes, click turn off to go back Offline.

3. Update or Re-enter the Account Details

1. Go to File > Account Settings > Manage Profiles.
2. Delete the existing Office 365 account and add to the system again.
3. Ensure that you are using the correct account credentials.
4. If Multi-factor authentication is enabled then complete the verification properly.

4. Clear and Recreate the OST File

A corrupted OST file is a major reason for Office 365 not syncing with outlook issues.

Steps:

1. Close Outlook.
2. Then, press Win + R and type- %localappdata%\Microsoft\Outlook\.
3. Delete the existing .ost file.
4. Outlook will automatically rebuild it.
5. Once done, Reopen Outlook and wait for it to resync all mailbox data.

5. Update Outlook and Windows Version

An outdated or old version of Outlook may cause compatibility issues with Office 365. As well as, an old Windows version can cause outlook sync issues.

In Outlook:
Go to File > Office Account > Update Options > Update Now.

In Windows:
Go to Settings > Windows Update > Check for Updates.

6. Check Microsoft 365 Service Status

• Visit the link– https://portal.office.com/servicestatus.
• If you see a red or orange alert that means Microsoft is fixing an outage. For that purpose you need to wait until it is resolved or fixed successfully.

Steps to Fix Office 365 Email Not Syncing with Outlook

1. Download and launch the above mentioned tool on your system.
2. Enter your Office 365 account details to Login.
3. After that, select all the files and folders to download.
   
4. Choose PST as the saving format.
   
5. Click on Start Backup to begin saving Office 365 data.
   
6. Once done, import these PST files into Outlook.
   Navigate to File > Open & Export > Import / Export > Import from another program or file (PST).

Core Features of the Pro Tool

• The tool quickly resolves Office 365 not syncing with Outlook by backing up all the data into a PST file for instant access.
• Fully compatible with all Outlook and Windows OS versions whether you are working on latest or old edition.
• The software guarantees maintaining original file structure and emails formatting throughout and even after the process is complete.
• Has the ability to download the entire mailbox in a single go without any data loss and saving valuable time.
• Apart from PST, it supports multiple file formats and emails clients such as EML, MBOX, PDF, MSG, and more. This will help you to share files across various platforms.
• Offer users dual file selection modes i.e. Select Files and Folders to allow users upload files as per their requirements.
• In addition, it supports advanced filter options based on date range, subject or keyword, sender, receiver details to more precisely save Office 365 emails.
• Generates a log report after completion which enables users to keep a track on the process as it includes all the details such as start date & time, saving type, destination path etc.

Prevent Outlook Sync Issues For Future

• Always keep Outlook and Windows updated in the latest version.
• Keep your mailbox size under control.
• Check Microsoft services if the syncing process stops suddenly.
• Avoid any shutdown or interruption while Outlook is running.
• Regularly repair and rebuild your Outlook OST files.

Conclusion

It is really tiring and tedious when your Office 365 not syncing with Outlook. I hope by the end you have got a reliable approach to overcome office 365 outlook synchronization errors or outlook sync issues. These manual fixes are okay but using the expert tool will offer you security as well as ease and future safety.

If you face any hindrance in using the tool or have some query, feel-free to contact our support team. They are available for you 24/7. You can directly email at [email protected] or have conversation at live chat support. We will make sure to resolve all your queries and provide you with the best solution.